Inner ear implant uses biological battery to self-charge

Implants that don't need an external charge could make it easy to aid hearing.

A team of surgeons, neuroscientists, and electrical engineers has developed a cochlea chip that extracts electrical signals from the inner ear to power itself.

The chip is the latest in a series of inventions aimed at creating entirely self-sufficient, self-powering implants that will remove the need for external power and enable permanent surgical implantation in some cases. This year alone, Stanford University announced the creation of its radio wave-powered heart implant and infrared light-powered retinal implants.

Cochlear implants have been around for decades, with the first electrical stimulation of auditory nerves taking place in the 50s. Though the implant has been a great success, with hundreds of thousands of people with severe hearing difficulties receiving the implant each year, they still run on batteries so are fairly cumbersome. MIT hopes to change all that by taking advantage of a natural battery that lies dormant within the ear.

"In the past, people have thought that the space where the high potential [in the ear] is located is inaccessible for implantable devices, because potentially it's very dangerous if you encroach on it," said Konstantina Stankovic, an otologic surgeon at the Massachusetts Eye and Ear Infirmary. "We have known for 60 years that this battery exists and that it's really important for normal hearing, but nobody has attempted to use this battery to power useful electronics."

Inside the ear chamber, negatively charged potassium ions and positively charged sodium ions are active either side of a membrane—this combination of ions helps convert the mechanical force of eardrum vibrations into electrochemical signals transmitted to the brain. It's this potential for electric charge Stankovic and her team are taking advantage of with their tiny electronic chips, fitted with several low resistance electrodes and a low-power radio transmitter. Although the inner ear is capable of producing a significant electrical current, it's still very low and the team could only extract a little so as to keep the charge low and not interfere with the hearing. Power-conversion circuitry was therefore also included to help power the low-energy chip.

The implant was tested on guinea pigs (their inner ears operate very much like humans'), with the electrodes attached to both sides of the cell membrane. Though the biological battery within the ear had the power to charge the chip, it needed a kick-start in the form of a radio wave burst. It took the capacitor between 40 seconds and four minutes to fill with enough energy to power the radio, after which time it ran without incident for up to five hours without affecting the guinea pigs' hearing, all the while transmitting chemical data to an external receiver.

The team hopes to make the devices even smaller and less invasive, since running them for long periods of time could mean damaging the inner tissue. But the results are promising and suggest that future cochlear implants could one day transmit vital biological and chemical statistics to monitor therapy progress, or even transmit the therapy itself.

Stankovic says the findings suggest there is a whole world of possibilities when it comes to using our own cells to self power devices. "A very futuristic view is that maybe we will be able to extract energy from individual cells using similar designs," she says.

I think it's a pretty neat combo of a unique biological environment and microelectronics. But can't help wondering whether muscle and piezoelectrics are a better marriage. And they could be external. But if internalization is really wanted, then how about a panic alarm transmitter hooked up to a piezoelectric transducer in the anal sphincter?

I think it's a pretty neat combo of a unique biological environment and microelectronics. But can't help wondering whether muscle and piezoelectrics are a better marriage. And they could be external. But if internalization is really wanted, then how about a panic alarm transmitter hooked up to a piezoelectric transducer in the anal sphincter?

I'd be looking to when we implant cells that can generate their own current from glucose and oxygen, separated by a semi permeable membrane to isolate them from our immune system.

This sort of thing is in development. But "isolating" something from the immune system is not easy, at least in the long term. If it were, bacteria wouldn't have such a tough time killing us. Most permeable membranes quickly ended up impermeable due to coating and attack by the immune system.

I am presuming that the Potassium ions are negative in relation to the Sodium ions present otherwise the sentence makes no sense.

This is a really interesting development for the hearing impaired. I would love to read the research article and see how the scientists have gotten the chips to actually use the EP energy. Too bad there is a paywall...

I'd be looking to when we implant cells that can generate their own current from glucose and oxygen, separated by a semi permeable membrane to isolate them from our immune system.

This sort of thing is in development. But "isolating" something from the immune system is not easy, at least in the long term. If it were, bacteria wouldn't have such a tough time killing us. Most permeable membranes quickly ended up impermeable due to coating and attack by the immune system.

Very easy to do if we use diamond as the semi-conductor. It's already made from carbon so the body doesn't see it as a foreign host.

I think it's a pretty neat combo of a unique biological environment and microelectronics. But can't help wondering whether muscle and piezoelectrics are a better marriage. And they could be external. But if internalization is really wanted, then how about a panic alarm transmitter hooked up to a piezoelectric transducer in the anal sphincter?

LOL... Your last sentence had me laughing so hard, I accidentally thumbed you down...sorry. I was, however, thinking the same thing about muscles and their greater potential energy-wise. Who knows, maybe even use an atrophied muscles' potential to power an artificial spider silk muscle system to overcome that muscles own weakness...

Instead of getting ones stomach stapled (or learning self control), just get some deceives installed that convert fat to energy. You could have it transmit energy to the couch, which would pass it on to the tv to help offset some of its power usage. One could be a real life "couch potato".

Instead of getting ones stomach stapled (or learning self control), just get some deceives installed that convert fat to energy. You could have it transmit energy to the couch, which would pass it on to the tv to help offset some of its power usage. One could be a real life "couch potato".

Interesting.But if any of you out there think that hearing aid batteries are going to become a thing of the past. Forget it.

There's a better chance of ink jet printers coming on the market that make their own ink.

That's not really relevant in this instance. Cochlear implants are a quite specialized class of hearing aid that are only used for very specific types of hearing loss that other hearing aid designs can't treat. Since they need to be powered one way or another, and by virtue of being surgically embedded can't trivially have their battery swapped, this kind of research is important. They're not going to be supplanting other hearing aid types either way since they can't cover the same issues that other CIC/ITE type designs can.

I am presuming that the Potassium ions are negative in relation to the Sodium ions present otherwise the sentence makes no sense.

Heh.. my biology students make the same mistake as the article all the time. Potassium and Sodium ions are equally "positive" - there's just a relatively greater concentration of positive ions outside the membrane than there are inside.

What they're describing is made to sound like something unique to the ear - they're just describing a common-garden-variety action potential, which happens in every single neuron in your body. Presumably they're just taking advantage of a higher-than-average neuron density in the ear than elsewhere.

I could see this with great potential for those in dangerous (audibly) professions or sports, like construction or shooting. An internal hearing device that mutes high decibel sounds while letting normal sounds through? It'd be worth the one-time cost to keep your hearing rather than always having to wear plugs, earmuffs or other devices, or have hearing damage from when you do those things *without* the protection (as can happen).